This invention relates to a mechanism used to move a magnetic recording head across a tape storage medium.
In the operation of microprocessor based computers such as those commonly known as "personal" computers, magnetically encoded data are often stored on a magnetic tape having recording tracks extending lengthwise on the tape. A tape drive system drives the tape past a magnetic read/write head which enters encoded information onto the tape in the write mode of operation and extracts data from the tape in the read mode. The magnetic recording head must be capable of precise adjustment across the width of the tape so that it can read from and write on all of the recording tracks.
Various types of mechanical devices have been used to move the recording head across the tape. Typically, a linear actuator or an electric stepping motor is used as the drive component of the device, and the drive component moves the recording head up and down across the tape through a gear train or other mechanical drive system. Because it is desirable for the tape drive unit to have a low profile, the motor or actuator normally has a horizontal orientation, and it is necessary to use bevel gears or a similar mechanism to translate the output from the actuator into the necessary vertical movement of the recording head.
One of the principal problems with existing mechanisms is the substantial space they occupy. When gear trains are employed, they take up considerable space because of the necessary center to center distance between the mating sets of gears. Gear backlash can also be a problem. Without undue expense, it is difficult to provide a gear transmission which accurately positions the recording head within acceptable limits of accuracy. Gear drive systems suffer from the further disadvantage of applying rotational forces and moments to the recording head, and this can lead to binding and misalignment problems.
The present invention is directed to an improved tape head movement mechanism which eliminates the problems that have plagued existing devices. In accordance with the invention, a linear actuator is accurately located on a molded plastic base of the unit. The output shaft of the actuator carries a cable connector having a socket for receiving a ball which is crimped onto one end of a stainless steel cable coated with nylon. The cable extends along an arcuate surface on the base which guides the cable through a gradual 90.degree. bend so that the end opposite the cable connector moves up and down when the actuator shaft is extended and retracted. The vertically oriented end of the cable carries a larger ball which is received in a pocket formed on an elevator bracket. The tape head is glued to the elevator bracket, and the bracket is accurately guided up and down along a pair of guide pins. A spring acting on the bracket maintains the cable under tension so that extension and retraction of the actuator shaft is translated into corresponding up and down movement of the recording head.
It is a particularly important feature of the invention that the guide pins are situated close to the tape head and to one another. The construction of the unit also permits the cable to connect with the elevator bracket at a location midway between the guide pins. Consequently, significant moments are not applied to the bracket, and the tendency for the bracket to bind is reduced in comparison to mechanisms in which the tape head is subjected to large moment forces. The cable drive arrangement is improved in comparison to gear drive systems because the cable applies no rotational forces to the tape head or bracket, so twisting is not a problem. At the same time, the mechanism achieves a one to one correlation between the movement of the actuator shaft and tape head, thus allowing the tape head to be precisely positioned on the tape.